Advanced Driver Assistance Systems (ADAS) employing image recognition techniques have been utilized in obstacle detection so as to notify vehicle drivers of obstacle(s) ahead, and even enables the vehicles to brake automatically to prevent collision. However, interference from headlight of approaching vehicles, dirt and dust on a lens of an image capturing device of the ADAS system, or a backlit object in an image captured by the image capturing device may cause mistakes during contour tracing or texture analysis, resulting in misleading results of obstacle detection.